1. Field of the Invention
The invention relates to an audio signal processing method, more particularly to a variable speed audio signal processing method and apparatus thereof.
2. Description of the Related Art
Time scaling is employed to change length of an audio signal data stream (i.e., change number of data points in an audio signal data stream) without affecting pitch, thereby changing playback speed.
Referring to FIGS. 1(a) and 1(b), time domain harmonic scaling (TDHS) is a frequently used time scaling technique that has the advantage of relatively low computational amount. An audio signal data stream includes a plurality of audio signal segments, and each audio signal segment includes a plurality of data points. As shown in FIG. 1(a), during playback at a relatively slow speed, an audio signal data section (S2) is found from an audio signal segment (S1) and audio signal data appended thereto. The audio signal data section (S2) is spliced to the audio signal segment (S1) to increase the length of the audio signal segment (S1). As shown in FIG. 1(b), during playback at a relatively fast speed, an audio signal segment (S3) and an audio signal segment (S4) are partly spliced together such that an overall length of the audio signal segments (S3, S4) is shortened.
However, in the TDHS technique, if the splice point and the splice segment were not chosen properly, the reproduced sound thus heard will be discontinuous or noise will be generated, thereby lowering the quality of the reproduced sound. Moreover, when an audio signal and a video signal are played back together, the signals must be synchronized regardless of playback at a relatively fast speed or a relatively slow speed so as to ensure that the sounds and images match each other. However, the TDHS technique cannot ensure that the length of an audio signal after change reaches a target length, thereby resulting in non-synchronicity between the sounds and images.